Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.
In a large bowl, combine melted butter and brown sugar.
Mix well until the mixture is smooth and glossy.
Add in the eggs, one at a time, mixing thoroughly after each addition.
Stir in the vanilla extract until well combined.
In another bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
If desired, fold in the chocolate chips.
Spread the batter evenly into the prepared baking pan.
Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.